Polycarbonates, being macromolecular polymers having carbonate groups in molecular chains, are fully-degradable macromolecular material having good transparency and oxygen and water barrier properties, which have been applied to various fields such as bio-degradable pollution free material, novel liquid-crystal material, gas barrier material, rubber material reinforcing agent and composite material.
So far, methods for synthesizing polycarbonates include phosgene method, ring-opening polymerization of cyclic carbonate, transesterification of small molecular carbonate; and copolymerization of carbon dioxide and an epoxy compound. Preparation of polycarbonates by phosgene method using phosgene and diol as starting materials will adversely affect ecological environment due to the use of highly toxic chemical, i.e. phosgene as starting material; in preparation of polycarbonates via ring-opening polymerization of cyclic carbonates, polycarbonates having relatively high molecular weight can be synthesized by ring-opening polymerization of six- or higher-membered cyclic carbonates, but environmental problem also occurs since cyclic carbonates are mostly prepared by phosgene method; in preparation of polycarbonates by transesterification of small molecular carbonate, polycarbonates having various structures can be synthesized by transesterification of small molecular diol with small molecular carbonate; and when polycarbonates are prepared by copolymerization of carbon dioxide and an epoxy compound, carbon dioxide and an epoxy compound are polymerized in the presence of a catalyst to obtain the polycarbonates. Since carbon dioxide is the main gas causing greenhouse effect and also an inexpensive source of carbon and oxygen, preparation of polycarbonates using copolymerization of carbon dioxide and an epoxy compound has advantages in terms of environmental protection and economic efficiency, therefore preparation of polycarbonates using this method is of great interest.
Polycarbonates are synthesized by copolymerization of carbon dioxide and an epoxy compound in the presence of a catalyst, in which the catalyst employed includes a series of catalysts such as alkyl zinc-active hydrogen catalytic system, zinc carboxylate catalytic system, zinc phenolate catalytic system, zinc diimine catalytic system, bimetal cyanide catalytic system, rare-earth ternary catalytic system and metalporphyrin catalytic system. Metalporphyrin catalytic system draws attention in the field of carbon dioxide-epoxy compound catalysts because porphyrin ligand is simple to be prepared, and has special spatial configuration of electrons and relatively strong capability of coordinating with metals, for example, Chinese Patent Publication No. CN 102558199A discloses a metalporphyrin complex for catalyzing polymerization reaction of carbon dioxide and an epoxy compound to prepare a polycarbonate. However, the metalporphyrin complex disclosed in the prior art has relatively low catalytic activity when catalyzing copolymerization reaction of carbon dioxide and an epoxy compound.